1. Field of the Invention
This invention relates to a so-called switch-type pushbutton tuner, and is particularly directed to construction of tuning shafts connected to individual pushbuttons.
2. Description of the Prior Art
Pushbutton tuners, in general, are used to tune a radio receiver, etc. at a broadcasting station by inserting a core movable simultaneously with a pushbutton in a coil. There is a so-called switch type pushbutton tuner as being one of said pushbutton tuners. This switch type pushbutton tuner is to effect tuning by pushing a desired one of several pushbuttons which outwardly protrude through a front face of the tuner. Each pushbutton has a tuning shaft integrally connected thereto so that when the pushbutton is rotated, the tuning shaft also rotates, thereby presetting a frequency to a pushbutton.
Such switch type pushbutton tuner, however, some time causes deviation of a frequency which is preset to a pushbutton due to careless rotation of the pushbutton upon pushing operation thereof because the tuning shaft is integrally connected to the pushbutton.
In this connection, there has been proposed a pushbutton tuner having clutch mechanism between a pushbutton and a tuning shaft so as not to rotate the tuning shaft even if the pushbutton is rotated except upon presetting a frequency, thereby preventing preset frequency deviation. Namely, a tuning shaft 1, as shown in FIG. 1, has at a front end (right end in the Figure) thereof a clutch shaft 2 configured in substantially elongated rectangular-shaped section. A pushbutton 3 to be engaged with the clutch shaft 2 has a clutch cavity 4 in a configuration corresponding to that of the section of the clutch shaft. When the clutch shaft 2 is inserted in the clutch cavity 4 and the clutch shaft 1 is integrally connected to the pushbutton 3, rotation of the pushbutton 3 is transmitted to the tuning shaft 1, so that an associated core enters in a coil to a depth corresponding to moving amount of a core slide which is urged by a screw member mounted on the tuning shaft 1, thereby selecting a desired frequency.
Upon tuning operation of a radio, in order to make the clutch shaft 2 at the front end of the tuning shaft 1 engage with the clutch cavity 4, length direction of the rectangles of the clutch shaft 2 and the clutch cavity 4 must coincide. To this end, it has been necessary to rotate the pushbutton about 180 degrees at maximum after pushing the same. This prevents prompt tuning operation because it is difficult to rotate the pushbutton 3 so large angle as 180 degrees by one hand.